Iframe Problem: Can Read Contents With InnerHTML, But Cannot Insert.

I can read the contents of an iframe:

HTML Code:
var iframe = document.getElementById("message");
var iframeContents = iframe.contentDocument.body.innerHTML;

var txtarea = document.getElementById('message2');
txtarea.value = iframeContents;
This will read the contents of an iframe, and write it to a textarea.
iframe is editable, and content is entered by the user. Still, this works.

But, below code is not working. Trying to put some content to an iframe, with the same innerHTML method above. It returns no errors or warnings. Even last alert() displays "<div>lorem ipsum</div>", but iframe is empty, it displays nothing..

HTML Code:
var textContent = "lorem ipsum";
var iframe2 = document.getElementById('message');
iframe2.contentDocument.body.innerHTML = '<div>'+textContent+'</div>'

alert(iframe.contentDocument.body.innerHTML);